The histogram is an excellent tool for photographers brought about by the digital age. If you're unfamiliar with it, the histogram is the small graph displayed on your camera's LCD screen, usually while in image review mode. This little-used graph can help you take better photographs, and can be utilized in just about any situation.

The information contained in the histogram is simply a visual representation of the tonal values recorded on an image. But how do you read this information? It's simple! The left side of the graph represents shadows and the right side are the highlights. If that's too difficult to remember, just think of black and white. Left=black and right=white.

Some graph displays show more information than others. For example, the D90 shows different color values. A high graph peak of red means there is a lot of that tonal value in the image. The same is true for other colors. If the histogram is pushed over to the right side of the graph, you have too much white, or an overexposed image. If all of the histogram is crammed against the left side of graph, it means that your photo is too dark, and underexposed. The camera may have rendered some portions as true black, which means a loss of detail and tonal information.

Ideally, you want a nice curving arc shape to your histogram. In mathematics, this is called a "bell curve". The right side (highlights) of the graph contains about 80-90% of the image information. This is especially important to remember if you do post-processing work using Lightroom or Photoshop. It is much easier to bring out details from highlights than it is from shadows. You will notice that with a properly exposed image, and a histogram that is arced to the right (but not overexposed!), your image files will be much larger because they contain higher degrees of detail. This is referred to as "shooting to the right".

So be sure to check your histogram! It can give you more clues about what you've captured than just a simple image review alone.

Definitely a great post. I've been doing this from the beginning, and it's good to see this subject brought up again, because it does indeed prevent a lot of wasted shots. I never go by the EV number anyway. The histogram is an awesome tool!

Also, I'd like to add a few other tips related to the histogram:

1. Be careful when shooting pictures that have a small area that is very bright (such as white birds or boats in a shot) because you might still get a nice bell curve, but there will be a tall, narrow spike on the right that signals you have burnt-out highlights.

2. With three- color histograms, if you clip the blue channel (blue histogram with a big right spike) and the other channels look ok, you will have a cyan (nasty!) sky on sunny days.

3. Likewise, when shooting sunsets, red is more likely to clip with a right spike, causing ugly yellow or red sploches around the sun.

4. If a shot looks good in the histogram(s), also check it in "highlight mode" (if your camera supports this playback option). Anything overexposed will repeatedly blink at you. I've used this to pick out washed-out areas in clouds, white birds, or boats, to name a few possibilities. Then I re-shoot down a half-stop or full stop, if necessary to capture that detail.

5. Another thing you can do to get better histograms is to (if your camera allows it) adjust your contrast. Usually, this is a custom setting, but if you have a scene with a wide dynamic range (the range of brightnesses), you can often prevent the dilemma of having to decide whether to overexpose highlights or black-out shadows. Just lower the contrast to a minimum on bright scenes with shadows, increase the contrast on foggy or cloudy days where there are few shadows and the light is more even-toned. The goal, as Anthony said, is a nice wide curved histogram with no peaks at either end.

I agree with Laurie Anne King, great presentation, I never understood the value of the histogram till now, now all I have to do is learn to use it to my advantage, if you don't mind I'll report back to you as to my progress, maybe next time my fireworks pics will be clearer.

I was shooting with a Photographer in Yellowstone last spring and he told me to hang to the right as the first 25% has 75% of the information. It is easier to correct after shot if your shot is hanging to the right as compared with the left of your histogram. Any thoughts. Thanks in advance, Ken